This invention relates generally to gas turbine engine rotors and, more particularly, to rotor protection systems to prevent a rotor over-speed condition.
Gas turbine engines typically include over-speed protection systems that provide rotor over-speed protection. Typically the over-speed protection systems either maintain rotor speed below critical rotor speeds or shut off fuel flow to an engine combustor. One type of known protection system receives signals indicative of rotor speed from mechanical speed sensors. The mechanical speed sensors include rotating flyweight sensing systems that indicate an over-speed condition as a result of the rotor rotating above the normal operational maximum speeds, yet below the structural failure limits. The flyweight sensing systems are hydro-mechanically coupled to a fuel bypass valve, and the fuel bypass valve reduces an amount of fuel that can be supplied to the engine if an overspeed condition is sensed.
Other types of known over-speed protection systems receive over-speed signal information from electronic control sensors. Known electronic controls derive over-speed conditions from such electronic control sensors. Such systems provide for rapid fuel shutoff and resulting engine shutdown if engine speed exceeds a normal maximum value.
In an exemplary embodiment, a gas turbine engine includes a rotor overspeed protection system to prevent the engine rotor from operating at a speed greater than a pre-set operational maximum speed. The engine rotor protection system is coupled to a fuel metering system that supplies fuel to the engine. The fuel metering system includes a fuel metering valve in flow communication with a fuel shutoff valve and a fuel bypass valve. The rotor protection system includes an overboost servovalve and a soleniod valve, and is coupled to an independent speed sensing system. The overboost servovalve includes a plurality of fuel ports.
In operation, when the independent sensing system senses a rotor overspeed condition, a signal is transmitted to the servovalve. The servovalve opens the flow ports in response to the overspeed signal to modify a control pressure signal from the fuel metering valve to the fuel bypass valve. Furthermore, as the servovalve is opened, a portion of fuel flowing to the fuel metering valve is diverted through the fuel bypass valve prior to entering the fuel metering valve. The fuel bypass valve is controlled in response to changes in fuel pressure created by flow through the servovalve; as the fuel bypass valve is opened, less fuel flows through the fuel metering valve. Thus, the servovalve controls the metered fuel flow to the engine independently of the fuel metering valve, and thus, facilitates reducing instances when the rotor operates at a speed greater than a pre-set operational maximum speed, known as an overspeed, or is accelerated with a boost greater than a pre-set operational maximum boost, known as an overboost. Furthermore, the servovalve can be used to shut the fuel shutoff valve, thus stopping fuel flow to the engine.